This invention generally relates to aircraft control systems and more particularly concerns fly-by-wire (FBW) aircraft or fly-by-light (FBL) control systems and even more particularly relates to fly-by-wire or light systems having manual override capabilities.
In the past, aircraft flight control systems have included mechanical linkage, such as cables, from the yoke in the cockpit to the control surfaces on the aircraft. Also, autopilots have been frequently coupled to the cables to automatically drive the control surfaces. One consequence of this mechanical linkage is that the yoke was correspondingly moved, by the cables, whenever the autopilot manipulated the cables to control the control surfaces. This was desirable because it provided the pilot with an indication of what the autopilot was doing.
In recent years, there has been a proposal to eliminate the heavy cables associated with the earlier flight control systems and replace them with a new fly-by-wire system where the yoke sends electronic signals along a signal line to an electronic servo at the control surface. It has also been proposed that an autopilot can be used to generate electronic commands which are sent along the signal lines to the control surfaces.
While this system would have several advantages, it also has several disadvantages. First of all, without the mechanical linkage between the autopilot and the yoke there is no indication to the pilot of what the autopilot is doing. Secondly, any manual override of the autopilot would likely result in switching from autopilot control to manual control and thereby creating a "bump" or disturbance of the control surfaces.
Consequently, there exists a need for improvement in flight control systems which incorporate fly-by-wire or fly-by-light technology and provide for manual override.